U.S. patent application number 12/934471 was filed with the patent office on 2011-05-12 for stack structure for laminated solid oxide fuel cell, laminated solid oxide fuel cell and manufacturing method.
This patent application is currently assigned to JAPAN FINE CERAMICS CENTER. Invention is credited to Fumio Hashimoto, Takayuki Hashimoto, Kaori Jono, Seiichi Suda.
Application Number | 20110111320 12/934471 |
Document ID | / |
Family ID | 41113958 |
Filed Date | 2011-05-12 |
United States Patent
Application |
20110111320 |
Kind Code |
A1 |
Suda; Seiichi ; et
al. |
May 12, 2011 |
STACK STRUCTURE FOR LAMINATED SOLID OXIDE FUEL CELL, LAMINATED
SOLID OXIDE FUEL CELL AND MANUFACTURING METHOD
Abstract
A stack structure for a solid oxide fuel cell includes a
plurality of stacked single cells, each having a fuel electrode
layer including a fuel electrode and an air electrode layer
including an air electrode, the fuel electrode layer and the air
electrode layer being arranged opposite each other on either side
of a solid electrolyte, separators arranged between the stacked
single cells to separate the single cells, and non-porous seal
parts located within the fuel electrode layer and the air electrode
layer, are equivalent to either the separators or the solid
electrolyte at least in terms of thermal expansion and contraction
characteristics, and are integrated with an edge of the fuel
electrode or an edge of the air electrode, and also with the
adjacent separator and the adjacent solid electrolyte.
Inventors: |
Suda; Seiichi; (Aichi,
JP) ; Jono; Kaori; (Aichi, JP) ; Hashimoto;
Fumio; (Aichi, JP) ; Hashimoto; Takayuki;
(Aichi, JP) |
Assignee: |
JAPAN FINE CERAMICS CENTER
NAGOYA-SHI, AICHI
JP
FCO CORPORATION
NAGOYA-SHI, AICHI
JP
|
Family ID: |
41113958 |
Appl. No.: |
12/934471 |
Filed: |
March 26, 2009 |
PCT Filed: |
March 26, 2009 |
PCT NO: |
PCT/JP2009/056188 |
371 Date: |
January 28, 2011 |
Current U.S.
Class: |
429/465 ;
429/535 |
Current CPC
Class: |
Y02P 70/50 20151101;
H01M 8/0263 20130101; H01M 2008/1293 20130101; H01M 8/0276
20130101; H01M 8/2425 20130101; H01M 8/0286 20130101; Y02E 60/50
20130101; H01M 8/2432 20160201; H01M 8/0282 20130101; H01M 8/2404
20160201 |
Class at
Publication: |
429/465 ;
429/535 |
International
Class: |
H01M 8/24 20060101
H01M008/24; H01M 8/00 20060101 H01M008/00; H01M 8/02 20060101
H01M008/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2008 |
JP |
2008-080794 |
Claims
1. A stack structure for a solid oxide fuel cell, comprising: a
plurality of stacked single cells, each having a fuel electrode
layer comprising a fuel electrode and an air electrode layer
comprising an air electrode, the fuel electrode layer and the air
electrode layer being arranged opposite each other on either side
of a solid electrolyte; separators arranged between the stacked
single cells to separate the single cells; and non-porous seal
parts that are located within the fuel electrode layer and the air
electrode layer, are equivalent to either the separators or the
solid electrolyte at least in terms of thermal expansion and
contraction characteristics, and are integrated with an edge of the
fuel electrode or an edge of the air electrode, and also with the
adjacent separator and the adjacent solid electrolyte, wherein the
stack structure is formed such that a stream of fuel gas is
supplied to the fuel electrode and a stream of air gas is supplied
to the air electrode respectively.
2. The stack structure according to claim 1, wherein thicknesses of
the solid electrolyte, the fuel electrode layer and the air
electrode layer in the single cell are each at least 1 .mu.m but no
more than 150 .mu.m.
3. The stack structure according to claim 1, wherein no single cell
support with enhanced mechanical strength is provided inside the
single cell.
4. The stack structure according to claim 1, wherein the seal parts
have a same composition as one of the separators and the solid
electrolyte.
5. The stack structure according to claim 1, wherein the seal parts
comprise a part of one of the separators and the solid electrolyte
that extends into the fuel electrode layer or the air electrode
layer.
6. The stack structure according to claim 1, wherein a unit
composed of the single cell and one or two of the separators that
are combined with the single cell has a flat overall shape.
7. The stack structure according to claim 1, wherein the separator
comprises a lanthanum-chromium perovskite oxide and rare
earth-doped zirconia.
8. A solid oxide fuel cell comprising the stack structure for a
solid oxide fuel cell according to claim 1.
9. A solid oxide fuel cell system comprising the stack structure
for a solid oxide fuel cell according to claim 1.
10. A method for manufacturing a laminated solid oxide fuel cell in
which single cells, each having a fuel electrode layer comprising a
fuel electrode and an air electrode layer comprising an air
electrode, the fuel electrode layer and the air electrode layer
being arranged opposite each other on either side of a solid
electrolyte, are stacked with separators in between to separate the
single cells, the method for manufacturing a laminated solid oxide
fuel cell comprising the steps of: preparing a laminate by
repeating the following steps (a) and (b); (a) preparing a first
sheet comprising a solid electrolyte material which is a material
of the solid electrolyte or a separator material which is a
material of the separator; (b) preparing a second sheet having an
electrode material region comprising a fuel electrode material or
an air electrode material and a seal material region for forming a
non-porous seal part that is equivalent to either the solid
electrolyte or the separators in terms of at least thermal
expansion and contraction characteristics, and laminating this
second sheet on the first sheet; and heat treating the
laminate.
11. The method for manufacturing a laminated solid oxide fuel cell
according to claim 10, wherein the seal material region of the
second sheet has a same composition as the first sheet.
12. The method for manufacturing a laminated solid oxide fuel cell
according to claim 10, wherein the second sheet is prepared by tape
casting.
13. The method for manufacturing a laminated solid oxide fuel cell
according to claim 12, wherein the second sheet is prepared by
simultaneously casting the electrode material region and the
non-porous material region.
14. The method for manufacturing a laminated solid oxide fuel cell
according to claim 10, wherein an evaporative material layer, which
has a pattern of a fuel gas conduit or an air gas conduit and is
composed of an evaporative material eliminated by the heat
treatment, is provided on the first sheet after the step (a) but
before the step (b).
15. The method for manufacturing a laminated solid oxide fuel cell
according to claim 10, wherein the separator material comprises a
lanthanum-perovskite oxide and rare earth-doped zirconia.
16. The stack structure according to claim 2, wherein no single
cell support with enhanced mechanical strength is provided inside
the single cell.
17. The stack structure according to claim 2, wherein the seal
parts have a same composition as one of the separators and the
solid electrolyte.
18. The stack structure according to claim 3, wherein the seal
parts have a same composition as one of the separators and the
solid electrolyte.
19. The stack structure according to claim 2, wherein the seal
parts comprise a part of one of the separators and the solid
electrolyte that extends into the fuel electrode layer or the air
electrode layer.
20. The stack structure according to claim 3, wherein the seal
parts comprise a part of one of the separators and the solid
electrolyte that extends into the fuel electrode layer or the air
electrode layer.
Description
TECHNICAL FIELD
[0001] The present teachings relates to a stack structure for a
laminated solid oxide fuel cell, and to a laminated solid oxide
fuel cell and a method of manufacturing the same.
BACKGROUND ART
[0002] In a solid oxide fuel cell (sometimes abbreviated below as
SOFC), a unit consisting of a fuel electrode, a solid electrolyte
and an air electrode is called a single cell, and a plurality of
these units is stacked to achieve a serial connection and construct
a power generating system. Tens to hundreds of single cells must be
stacked to obtain adequate power output, and the single cells must
be mechanically strong enough to provide stable, long-term power
generation in such a highly stacked state. For this reason, it is
common to use electrolyte-supported cells comprising a solid
electrolyte hundreds of microns thick with a fuel electrode and air
electrode tens of microns thick printed on either side of the solid
electrolyte.
[0003] In order to improve a power generating characteristics of a
single cell and consequently the power generating characteristics
of a stack, it is necessary to minimize an internal resistance of
the single cell. Because the electrolyte has the highest resistance
of the components of the single cell, research has been conducted
for reducing the thickness of the solid electrolyte (e.g. Patent
Document 1).
[0004] There has therefore been research into electrode-supported
cells, in which the solid electrolyte is made thinner while the
thickness of the air electrode and fuel electrode, which have
relatively less internal resistance than the solid electrolyte, is
increased from hundreds of microns to a few millimeters (e.g.
Patent Document 2). [0005] Patent Document 1 Japanese Patent
Application Publication No. 2003-346842 [0006] Patent Document 2
Japanese Patent Application Publication No. 2005-85522
SUMMARY OF INVENTION
[0007] In an electrode-supported cell, the mechanical strength is
provided by the electrodes, which are porous and must thus be
relatively thick in order to ensure the necessary mechanical
strength. Although reducing the thickness of the solid electrolyte
reduces the internal resistance of the solid electrolyte itself,
moreover, the internal resistance of the electrodes is increased
concomitantly, and so the desired improvement in power generating
characteristics has yet to be achieved.
[0008] In any case, the aforementioned prior art is aimed at
ensuring the mechanical strength of the single cell unit.
Consequently, the mechanical strength is secured by means of the
thickness of some component of the single cell, and a thermal shock
resistance declines due to differences in the thermal expansion
rates of the components. Up to now, no SOFC stack structure has
been provided to solve these problems.
DISCLOSURE OF THE INVENTION
[0009] It is therefore an object of the present teachings to
provide a laminated SOFC having a stack structure capable of
ensuring the mechanical strength of the SOFC as a whole without
relying on the mechanical strength of the single cells. It is
another object of the present teachings to provide a laminated SOFC
having a stack structure capable of effectively reducing internal
resistance to provide good power generating characteristics. It is
another object of the present teachings to provide a laminated SOFC
having a stack structure capable of improving thermal shock
resistance. It is still another object of the present teachings to
provide a laminated SOFC having a stack structure that can be
easily stacked. It is yet another object of the present teachings
to provide a manufacturing method for manufacturing such a
laminated SOFC.
[0010] Abandoning the conventional wisdom of "ensuring the
mechanical strength of the single cell", the inventors discovered
that if the mechanical strength of the SOFC as a stack structure
can be ensured, it is possible to construct the SOFC structure
without being constrained by the thickness of the electrodes, solid
electrolyte and other cell components in order to ensure the
mechanical strength of each single cell. The inventors perfected
the present teachings based on this discovery. The followings may
be provided by the present teachings.
[0011] The present teachings may provide a stack structure for a
solid oxide fuel cell, comprising: a plurality of stacked single
cells, each having a fuel electrode layer comprising a fuel
electrode and an air electrode layer comprising an air electrode,
the fuel electrode and the air electrode being arranged opposite
each other on either side of a solid electrolyte; separators
arranged between the stacked single cells to separate the single
cells; and seal parts comprising non-porous parts that are located
within the fuel electrode layer and the air electrode layer, are
equivalent to either the separators or the solid electrolyte at
least in terms of thermal expansion and contraction
characteristics, and are integrated with an edge of the fuel
electrode or an edge of the air electrode, and also with the
adjacent separator and the adjacent solid electrolyte, wherein the
stack structure is formed such that a stream of the fuel gas is
supplied to the fuel electrode and a stream of the air gas is
supplied to the air electrode respectively.
[0012] In the stack structure of the present teachings, thicknesses
of the solid electrolyte, the fuel electrode layer and the air
electrode layer in the single cell are each preferably at least 1
.mu.m but no more than 150 .mu.m. When the thicknesses of these
elements are within this range, they can be easily integrated to
form a single cell. It is also possible to ensure the strength of
the stack structure formed by stacking these single cells. No
single cell support with enhanced mechanical strength is preferably
provided inside the single cell. This is because providing the
single cell support with enhanced mechanical strength actually
makes it more difficult to construct the stack structure. The seal
parts preferably have a same composition as one of the separators
and the solid electrolyte. The seal parts preferably comprise a
part of one of the separators and the solid electrolyte that
extends into the fuel electrode layer or the air electrode layer.
In this stack structure, a unit composed of the single cell and one
or two of the separators that are combined with the single cell may
have a flat-plate overall shape. The separator preferably contains
a lanthanum-chromium perovskite oxide and rare earth-doped
zirconia. Preferably, it consists only of these.
[0013] The present teachings may provide a solid oxide fuel cell
having the above-described stack structure for the solid oxide fuel
cell. The present teachings may also provide a solid oxide fuel
cell system provided with the above-described stack structure for
the solid oxide fuel cell.
[0014] The present teachings may provide a method for manufacturing
a laminated solid oxide fuel cell in which single cells each having
a fuel electrode layer comprising a fuel electrode and an air
electrode layer comprising an air electrode, the fuel electrode
layer and the air electrode layer being arranged opposite each
other on either side of a solid electrolyte, are stacked with
separators in between to separate the single cells, the method
includes the steps of: preparing a laminate by repeating the
following steps (a) and (b);
[0015] (a) preparing a first sheet containing a solid electrolyte
material which is a material of the solid electrolyte or a
separator material which is a material of the separator;
[0016] (b) preparing a second sheet having an electrode material
region comprising a fuel electrode material or an air electrode
material and a non-porous material region for forming a non-porous
seal part that is equivalent to either the solid electrolyte or the
separators in terms of at least thermal expansion and contraction
characteristics, and laminating this second sheet on the first
sheet; and
[0017] heat treating the laminate.
[0018] In the manufacturing method of the present teachings, the
non-porous material region of the second sheet preferably has a
same composition as the first sheet. This second sheet is
preferably prepared by tape casting. The second sheet is also
preferably prepared by simultaneously casting the electrode
material region and the non-porous material region. An evaporative
material layer, which has a pattern of a fuel gas conduit or an air
gas conduit and is composed of an evaporative material eliminated
by the heat treatment, is preferably provided on the first sheet
after the step (a) but before the step (b). The separator material
preferably contains a lanthanum-chromium perovskite oxide and
rare-earth doped zirconia.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows one example of a stack structure for a
laminated SOFC of the present teachings.
[0020] FIG. 2 shows another example of the stack structure for the
laminated SOFC of the present teachings.
[0021] FIG. 3 shows another example of the stack structure for the
laminated SOFC of the present teachings.
[0022] FIG. 4 shows a manufacturing process for the stack structure
for the laminated SOFC of the present teachings.
[0023] FIG. 5 shows one example of the manufacturing process for
the stack structure for the laminated SOFC of the present
teachings.
[0024] FIG. 6 shows a cross-section of a structure obtained by
firing.
[0025] FIG. 7 shows results of EDX evaluation of compositions of
the cross-sections of the structures obtained by the firing.
[0026] FIG. 8 shows measurement results for density of sintered
bodies obtained by firing.
[0027] FIG. 9 shows results of SEM observation of cross-sections of
the resulting sintered bodies (YSZ 0 mass % and 1 mass %
samples).
REFERENCE SIGNS LIST
[0028] 2 Single cell, 4 Solid electrolyte, 6 Fuel electrode layer,
7 Fuel electrode, 8 Air electrode layer, 9 Air electrode, 10a, 10b,
30a, 30b, 50a, 50b Seal parts, 14 Separator, 16, 36 Fuel gas
conduits, 17, 37a, 37b Openings, 18, 38 Air gas conduits, 19, 39a,
39b Openings, 20, 40, 60 Stack structures
DESCRIPTION OF EMBODIMENTS
[0029] The present teachings relate to a stack structure for a
laminated SOFC, to a laminated SOFC provided with this stack
structure, to an SOFC system provided with this laminated SOFC, to
a method for manufacturing a laminated SOFC, and to an electrode
sheet with integrated gas seal region and a manufacturing method
therefor.
[0030] Certain embodiments of the present teachings provide a stack
structure provided with a plurality of stacked single cells, each
having a fuel electrode layer comprising a fuel electrode and an
air electrode layer comprising an air electrode arranged opposite
each other on either side of a solid electrolyte, with separators
separating the stacked single cells, and provided especially with
seal parts that are located within the fuel electrode layer and the
air electrode layer, are equivalent to either the separator or the
solid electrolyte at least in terms of thermal expansion and
contraction characteristics, and are integrated with the edge of
the fuel electrode or the edge of the air electrode and also with
the adjacent separator and solid electrolyte. The stack structure
is formed such that a stream of the fuel gas is supplied to the
fuel electrode and a stream of the air gas is supplied to the air
electrode. Other embodiments of the present teachings can also be
directed to such a stack structure.
[0031] With the stack structure of the present teachings, when the
features described above are adopted including the seal parts,
which are equivalent to the separator or solid electrolyte in terms
of thermal expansion and contraction characteristics, passage of
fuel gas is separated from passage of air gas by means of the seal
parts. With the stack structure of the present teachings, moreover,
a structure may be achieved in which a continuous phase of
separators and solid electrolytes integrated via seal parts is
formed throughout the stacked single cells, with the fuel
electrodes and air electrodes filling the spaces in this continuous
phase. Consequently, adequate mechanical strength can be easily
ensured by laminating to form the stack structure even if the
components of each single cell, i.e. the solid electrolyte, fuel
electrode and air electrode are all too thin to ensure the strength
of the individual single cell. That is, cell supports are not
needed to ensure mechanical strength as in an electrolyte-supported
or electrode-supported cell, and the various restrictions needed to
ensure the strength of the single cell can be avoided or
reduced.
[0032] Because the seal parts are equivalent to the solid
electrolyte or separator in terms of thermal expansion and
contraction characteristics, the aforementioned continuous phase
will have good heat shock resistance. Further, providing such seal
parts in the fuel electrode layer and air electrode layer serves to
mitigate the difference in thermal expansion and contraction
characteristics between the fuel electrode and air electrode on the
one hand and the solid electrolyte and separators on the other,
thereby improving heat shock resistance.
[0033] Moreover, the internal resistance and thermal expansion
coefficient can be fully determined when establishing the
thicknesses of the solid electrolyte, fuel electrode and air
electrode because these thicknesses are not constrained by the need
to ensure the mechanical strength of the single cell. As a result,
it may be possible to effectively reduce the internal resistance of
the stack structure, and improve the power generating
characteristics. It may also be possible to effectively improve the
heat shock resistance of the stack structure.
[0034] With the stack structure of the present teachings, moreover,
stacking is easy because the cells are laminated with seal parts
that can separate the streams of fuel gas and air gas are provided
within the fuel electrode layer and air electrode layer.
[0035] In the method for manufacturing a laminated SOFC of the
present teachings, a stack structure of single cells separated by
separators can be formed by preparing first sheets each consisting
of a solid electrolyte material or separator material and second
sheets each having an electrode material region and a seal part
material region, and laminating the sheets together. Consequently,
it is easy to manufacture the laminated SOFC of the present
teachings.
[0036] The various embodiments of the present teachings are
explained below with reference to the relevant drawings. FIG. 1
shows one example of the stack structure for laminated SOFCs of the
present teachings, FIG. 2 shows another example, FIG. 3 shows still
another example, and FIG. 4 shows one example of the SOFC
manufacturing process of the present teachings. Elements that are
common to these drawings are explained using the same symbols. The
stack structure for laminated SOFCs shown in these drawings is only
one example of the stack structure of the present teachings, and
the present teachings is not limited thereby. The same applies to
the SOFC manufacturing process.
(Stack Structure for Laminated SOFC)
[0037] The stack structure of the present teachings may take
various forms, but hereinbelow the stack structure of the present
teachings is explained with reference to FIGS. 1 through 3.
[0038] A stack structure 20 shown in FIG. 1 is provided with single
cells 2, separators 14, which are placed between stacked single
cells 2 to separate single cells 2, fuel gas conduits 16 for
supplying fuel gas to fuel electrodes 7, and air gas conduits 18
for supplying air gas to air electrodes 9. As shown in FIG. 1, each
single cell 2 comprises a solid electrolyte 4, a fuel electrode
layer 6 and an air electrode layer 8. The single cells 2 in the
present teachings are neither electrolyte supported nor electrode
supported. In the single cell 2 in the stack structure 20 of the
present teachings, the thicknesses of the fuel electrode layer 6
and air electrode layer 8 may e.g. each be at least 30% but no more
than 300% of the thickness of the solid electrolyte 4. Within this
range, warpage and peeling are unlikely to occur during firing.
[0039] The solid electrolyte 4 is formed as a layer having a planar
form similar to the planar form of the stack structure 20. The
planar form may be square, rectangular, circular or some other form
depending on the shape of the stack structure 20. The solid
electrolyte 4 may be a known electrolyte commonly used in SOFCs.
Examples include ceria oxides doped with samarium or gadolinium,
lanthanum-gallate oxides doped with strontium or magnesium,
zirconia oxides containing scandium or yttrium and other oxide ion
conducting ceramics materials.
[0040] The thermal expansion coefficient (between 20.degree. C. to
1000.degree. C.) of the solid electrolyte 4 is preferably between
10.times.10.sup.-6 K.sup.-1 and 12.times.10.sup.-6 K.sup.-1. Within
this range, peeling and cracking are unlikely to occur during
firing. 10.5.times.10.sup.-6 K.sup.-1 to 11.5.times.10.sup.-6
K.sup.-1 is more desirable considering the residual stress of the
stack structure.
[0041] The thickness of the solid electrolyte 4 is not particularly
limited, but can be at least 1 .mu.m but no more than 150 .mu.m.
Within this range, suitable mechanical strength and power
generating characteristics can be obtained when the single cell 2
is formed with the fuel electrode layer 6 and air electrode layer 8
as described below, and when the stack structure 20 is formed with
the separators 14. At least 1 .mu.m but no more than 100 .mu.m is
more desirable, at least 1 .mu.m but no more than 40 .mu.m is still
more desirable, and at least 1 .mu.m but no more than 20 .mu.m is
especially desirable.
[0042] The fuel electrode layer 6 contains a fuel electrode 7. For
the fuel electrode material composing the fuel electrode 7,
materials used as the fuel electrode materials in well-known SOFCs
can be used without any particular limitations. Examples include
mixtures of metal catalysts with ceramic powder materials
consisting of oxide-ion conductors, and composite powders thereof.
Examples of metal catalysts that can be used in this case include
nickel, iron, cobalt, precious metals (platinum, ruthenium,
palladium and the like) and other materials that are stable in
reducing atmospheres and have hydrogen oxidation activity.
Oxide-ion conductors having fluorite type structures or perovskite
structures can be used by preference as oxide-ion conductors.
Examples of those having fluorite type structures include ceria
oxides doped with samarium or gadolinium, zirconia oxides doped
with scandium or yttrium and the like. Examples of those having
perovskite structures include lanthanum-gallate oxides doped with
strontium or magnesium and the like. Of these materials, the fuel
electrode 7 is preferably formed from a mixture of nickel and an
oxide-ion conductor. Of the aforementioned ceramic materials, one
may be used alone or a mixture of two or more can be used. The fuel
electrode 7 can also be composed of a metal catalyst by itself. The
average particle diameter of the fuel electrode material is
preferably at least 10 nm but no more than 100 .mu.m, or more
preferably at least 50 nm but no more than 50 .mu.m, or still more
preferably at least 100 nm but no more than 10 .mu.m. The average
particle diameter can be measured e.g. in accordance with JIS
R1619. Like the solid electrolyte 4, the fuel electrode layer 6 can
be formed as a layer in accordance with the planar shape of the
stack structure 20.
[0043] The thermal expansion coefficient (between 20.degree. C. to
1000.degree. C.) of the fuel electrode layer 6 is preferably at
least 10.times.10.sup.-6 K.sup.-1 but no more than
12.5.times.10.sup.-6 K.sup.-1. Within this range, peeling is
unlikely to occur at the boundary with the solid electrolyte. At
least 10.times.10.sup.-6 K.sup.-1 but no more than
12.times.10.sup.-6 K.sup.-1 is more desirable taking into
consideration the residual stress of the stack structure. The
thickness of the fuel electrode layer 6 is not particularly
limited, but is preferably at least 1 .mu.m but no more than 150
.mu.m. Within this range, suitable mechanical strength and power
generating characteristics can be obtained when configuring the
single cell 2 and when configuring the stack structure 20 together
with the separators 14. At least 1 .mu.m but no more than 100 .mu.m
is preferable, at least 5 .mu.m but no more than 40 .mu.m is more
preferable, and at least 5 .mu.m but no more than 20 .mu.m is still
more preferable. In addition to the fuel electrode 7, the fuel
electrode layer 6 comprises a seal part 10a, which is discussed
below.
[0044] The air electrode layer 8 contains an air electrode 9.
Materials used as the air electrode materials in solid oxide fuel
cells can be used for the air electrode material composing the air
electrode 9, without any particular limitations. For example, metal
oxides with perovskite structures and the like made up of Co, Fe,
Ni, Cr or Mn or the like can be used. Specific examples include
(Sm,Sr)CoO.sub.3, (La,Sr)MnO.sub.3, (La,Sr)CoO.sub.3,
(La,Sr)(Fe,Co)O.sub.3 and (La,Sr)(Fe,Co,Ni)O.sub.3 oxides and the
like. (La,Sr)MnO.sub.3 is preferred. One of the aforementioned
ceramic materials can be used alone, or two or more may be used in
combination. The average particle size of a powder of the air
electrode material is preferably at least 10 nm but no more than
100 .mu.m, or more preferably at least 50 nm but no more than 50
.mu.m, or still more preferably at least 100 nm but no more than 10
.mu.m.
[0045] The thermal expansion coefficient (between 20.degree. C. to
1000.degree. C.) of air electrode layer 8 is preferably at least
10.times.10.sup.-6 K.sup.-1 but no more than 15.times.10.sup.-6
K.sup.-1. Within this range, peeling is unlikely to occur at the
boundary with the solid electrolyte. At least 10.times.10.sup.-6
K.sup.-1 but no more than 12.times.10.sup.-6 K.sup.-1 is preferred
from the standpoint of the residual stress of the stack structure.
The thickness of the air electrode layer 8 is not particularly
limited, but is preferably at least 1 .mu.m but no more than 150
.mu.m. Within this range, suitable mechanical strength and power
generating characteristics can be obtained when configuring the
single cell 2 and then when configuring the stack structure 20 with
the separators 14. At least 1 .mu.m but no more than 100 .mu.m is
preferred, at least 5 .mu.m but no more than 40 .mu.m is more
preferred, and at least 5 .mu.m but no more than 20 .mu.m is
especially preferred. In addition to the air electrode 9, the air
electrode layer 8 comprises a seal part 10b, which is discussed
below.
[0046] The thicknesses of the solid electrolyte 4, air electrode
layer 6 and fuel electrode layer 8 are preferably all at least 1
.mu.m but no more than 150 .mu.m. If all these elements are within
this range of thickness, differences in the thermal expansion and
contraction characteristics during firing or use can be adjusted
without any great restrictions when integrating these elements to
form a single cell. Because such integrated single cells can be
formed in this way, it is easy to ensure the strength of a stack
structure formed by laminating these single cells. More preferably,
all elements are at least 1 .mu.m but no more than 100 .mu.m thick.
Still more preferably they are no more than 40 .mu.m thick, and
ideally they are no more than 20 .mu.m thick. In this Description,
average particle sizes are measured e.g. in accordance with JIS
R1619.
[0047] In the stack structure 20, a plurality of single cells 2 are
laminated with the separators 14 separating the single cells. The
separators 14 are preferably in a flat-plate form that can be
laminated in the same way as the solid electrolyte 4, fuel
electrode layer 6 and air electrode layer 8. This is because such
flat separators are easy to prepare and do not necessitate a
complex lamination process in order to obtain the stack structure
20. Various known conductive materials used as SOFC separators can
be used as the material of the separators 14. In addition to
stainless metal materials, e.g., lanthanum chromite metal ceramics
can also be used.
[0048] As discussed below, the various components of the single
cells and separators 14 are preferably fired together and then
co-sintered to obtain the stack structure 20 of the present
teachings. In this embodiment, the separators 14 are preferably
made of a ceramic material that is sintered at relatively low
temperatures. For purposes of improving sinterability,
lanthanum-chromium oxide (LaCrO.sub.3),
lanthanum-strontium-chromium oxide (La.sub.(1-x)Sr.sub.xCrO.sub.3,
0<x.ltoreq.0.5) and other lanthanum-chromium perovskite oxides,
or ceramics comprising such lanthanum-chromium perovskite oxides
and rare-earth doped zirconia, are preferably used as such ceramic
materials. The lanthanum-chromium perovskite oxide can be sintered
more densely and at a lower temperature than in the past if rare
earth-doped zirconia (general formula
(1-x)ZrO.sub.2.xY.sub.2O.sub.3, wherein Y is a rare earth element
and 0.02.ltoreq.x.ltoreq.0.20) is included during firing. As a
result, the separators can be densified at a temperature of no more
than about 1400.degree. C., which is low enough to allow
co-sintering of the cell components. Such a lanthanum-chromium
perovskite oxide can also be doped with other metal elements.
[0049] Examples of the rare earth element in the rare earth doped
zirconia include yttrium (Y), scandium (S), ytterbium (Yb), cerium
(Ce), neodymium (Nd), samarium (Sm) and the like, of which yttrium
(Y), scandium (Sc) and ytterbium (Yb) are preferred, and yttrium
(Y) is especially preferred. The x in the rare earth doped zirconia
(general formula (1-x)ZrO.sub.2.xY.sub.2O.sub.3, where Y is a rare
earth element) is preferably at least 0.02 but no more than 0.2, or
more preferably at least 0.02 but no more than 0.1.
[0050] The thermal expansion coefficient (between 20.degree. C. to
1000.degree. C.) of the separator 14 is preferably at least
8.times.10.sup.-6 K.sup.-1 but no more than 12.times.10.sup.-6
K.sup.-1. Within this range, it is possible to control peeling with
the air electrode layer or fuel electrode layer. Considering the
residual stress of the stack structure, at least
9.5.times.10.sup.-6 K.sup.-1 but no more than 11.5.times.10.sup.-6
K.sup.-1 is especially preferred. The thickness of the separator 14
is not particularly limited, but is preferably at least 1 .mu.m but
no more than 200 .mu.m. Within this range, suitable mechanical
strength and power generating characteristics can be obtained when
the single cells 2 are stacked with separation to configure the
stack structure 20. At least 10 .mu.m but no more than 50 .mu.m is
preferred, and at least 10 .mu.m but no more than 40 .mu.m is more
preferred.
[0051] The thickness of each of the layers, including the
separators 14 and the components of the single cells, is preferably
no more than 100 .mu.m.
(Seal Part in Fuel Electrode Layer)
[0052] The fuel electrode layer 6 is provided with the seal part
10a in addition to the fuel electrode 7. The fuel electrode layer 6
has the seal part 10a within the range of thickness of the fuel
electrode layer 6. Preferably, it has a seal part 10a with a
thickness matching that of the fuel electrode layer 6. The seal
part 10a is integrated on the edge of the fuel electrode 7, with
the entirety thereof constituting the fuel electrode layer 6. The
seal part 10a is formed with sufficient non-porosity to provide
gas-tightness at least with respect to air gas and fuel gas as
required in the SOFC, and is formed so as to allow independent
streams of the fuel gas and air gas so that fuel electrode 7 of
fuel electrode layer 6 is not exposed to the air gas supplied to
its counter-electrode, the air electrode 9. Consequently, where the
seal is formed on the edge of the fuel electrode 7 depends on the
patterns of a fuel gas conduit 16 and an air gas conduit 18, and on
the arrangement of these two supply parts 16 and 18 within the
stack structure 20. More specifically, the seal part 10a is formed
on the edge on the same side as an opening 19 of the air gas supply
part 18, to prevent exposure of the fuel electrode 7 to the air
gas.
[0053] In the embodiment shown in FIG. 1, the fuel gas conduit 16
and air gas conduit 18 both have a pattern of a plurality of
u-shaped channels, with openings 17 and openings 19 opening,
respectively, only on a surface A and a surface B on opposite sides
of the stack structure 20. Consequently, in the embodiment shown in
FIG. 1 the edge of the fuel electrode layer 6 having the seal part
10a is the edge of the fuel electrode 7 on the surface B of the
stack structure 20.
[0054] For example, when the fuel gas conduit 36 and the air gas
conduit 38 are straight as in the stack structure 40 shown in FIG.
2, the gas openings 37a and 37b open onto opposing surfaces of the
stack structure 40, as do the openings 39a and 39b. That is, the
openings 39a, 39b open onto a surface C and a surface D of the
structure 40. For this reason, the seal parts 30a are provided
integrally on the edge of the fuel electrode 7 on the C and D
surfaces of the stack structure 40.
[0055] The seal part 10a is formed so as to be equivalent to the
separator 14 or solid electrolyte 4 at least in terms of the
thermal expansion and contraction characteristics. Accordingly,
differences in the thermal expansion and contraction
characteristics between the materials to be laminated are avoided
when separating the single cells with the separators 14 or when
configuring the single cell 2 with the fuel electrode layer 6, and
it is possible to obtain a stack structure 20 with excellent
integrity and heat shock resistance. The thermal expansion and
contraction characteristics include at least the thermal expansion
coefficient. "Equivalent" means that the thermal expansion and
contraction characteristics are the same as those of the separator
14 or solid electrolyte 4, or are within a range that does not
greatly affect the integrity of the stack structure 20 within the
range of temperatures applied to the SOFC during preparation and
operation of the SOFC. Experiments by the inventors have shown that
the integrity of the stack structure 20 will not be greatly
affected if the thermal expansion coefficient is at least 0.85
times but no more than about 1.18 times the thermal expansion
coefficient of the separator 14 or solid electrolyte 4.
[0056] The thermal expansion and contraction characteristics of the
seal part 10a may be equivalent to those of one of the separator 14
and solid electrolyte 4. If they are equivalent to one or the
other, peeling can be avoided at the boundary between the seal part
and either the separator 14 or solid electrolyte 4. Depending on
the thermal expansion coefficients of the separator 14 and solid
electrolyte 4, the thermal expansion and contraction
characteristics of the seal part 10a may be equivalent to the
thermal expansion and contraction characteristics of both the solid
electrolyte 4 and separator 14. This is most desirable from the
standpoint of improving the mechanical strength and heat shock
resistance of the stack structure 20.
[0057] The seal part 10a preferably has the same composition as one
of the separator 14 or solid electrolyte 4. With the same
composition, good integration can be achieved when the seal is
integrated with one of these, improving the heat shock resistance
of the stack structure 20 as well as the mechanical strength. When
the seal part 10a has the same composition as one of the separator
14 or solid electrolyte 4, the seal part 10a may actually comprise
a part of one of the separator 14 or solid electrolyte 4, or
consist of such a part. This means in other words that the seal
part 10a is composed of that the part of the separator 14 or solid
electrolyte 4 that extends into the fuel electrode layer 6, which
is a part excluding a part thereof that has reached into the fuel
electrode 7.
[0058] For example, in the stack structure 20 shown in FIG. 1 and
the stack structure 40 shown in FIG. 2, the seal parts 10a and 30a
each have the same composition as the solid electrolyte 4, and
consist of a part of the solid electrolyte 4. The seal part 50a of
the stack structure 60 shown in FIG. 3 has the same composition as
the separator 4, and consists of a part of the separator 4.
[0059] As shown in FIG. 2, when the seal parts 30a and 30b are
provided at the edges on both sides of the fuel electrode 7 and air
electrode 9 of the fuel electrode layer 6 and air electrode layer
8, the thermal expansion and contraction characteristics of the
seal part 30a can be equivalent to those of one of the separator 14
and solid electrolyte 4. If they are equivalent to one or the
other, peeling can be prevented at the boundary between the seal
part and the separator 14 or solid electrolyte 4. Depending on the
thermal expansion coefficients of the separator 14 and solid
electrolyte 4, the thermal expansion characteristics of the seal
parts 30a may be equivalent to the thermal expansion and
contraction characteristics of both the solid electrolyte 4 and
separator 14. This is most desirable from the standpoint of
improving the mechanical strength and heat shock resistance of the
stack structure 40.
(Seal Part in Air Electrode Layer)
[0060] The air electrode layer 8 is provided with the seal part 10b
in addition to the air electrode 9. The air electrode layer 8 has
the seal part 10b within the range of thickness of the air
electrode layer 8. Preferably, it has the seal part 10b with a
thickness matching that of the air electrode layer 8. Like the seal
part 10a, the seal part 10b is integrated on the edge of the air
electrode 7, with the whole composing the air electrode layer 8.
The seal part 10b is formed so as to avoid exposure of the air
electrode 9 to fuel gas, and ensure the independent passage of fuel
gas and air gas. The seal part 10b can take the same form as the
seal part 10a except that the seal part 10b prevents exposure of
the air electrode 9 to the fuel gas, while the seal part 10a
prevents exposure of the fuel electrode 9 to the air gas. That is,
it is possible to apply the various features explained above with
respect to the non-porosity of the seal part 10a, air electrode
layer 8 and the thermal expansion coefficient.
[0061] The seal part 10b may also have the same composition as one
of the solid electrolyte 4 and separator 14, or may comprise a part
thereof, but when the seal part 10a is the same as or constitutes a
part of one of these, the seal part 10b is preferably composed in
the same way as the seal part 10a. In this configuration, it is
possible to prevent deformation of the stack structure by thermal
expansion and contraction of the seal parts.
[0062] As in the case of the seal part 10a, the location of the
seal part 10b in the air electrode 9 or stack structure 20 depends
on the patterns of the fuel gas conduit 16 and air gas conduit 18,
and on the arrangement of these two supply parts 16 and 18 within
the stack structure 20. Specifically, the seal part 10b is formed
on the edge on the same side as the opening 17 of the fuel gas
supply part 16, to prevent exposure of the air electrode 9 to the
fuel gas.
[0063] In the embodiment shown in FIG. 1, the fuel gas conduit 16
and air gas conduit 18 both have a pattern of a plurality of
u-shaped channels, with the openings 17 and openings 19 opening,
respectively, only on the surface A and surface B on opposite sides
of the stack structure 20. Consequently, in the embodiment shown in
FIG. 1 the edge of the air electrode layer 8 having the seal part
10b is the edge of the air electrode 9 on the surface A of the
stack structure 20.
[0064] For example, in the stack structure 40 shown in FIG. 2, the
fuel gas openings 37a, 37b open onto the A and B sides of structure
40. Consequently, the seal parts 30b are integrally provided on the
edges of the air electrode 9 on the A and B sides of the stack
structure 40.
[0065] The laminated SOFC of the present teachings can be composed
of the stack structure of any of the various modes explained above.
For example, a laminated SOFC can be configured by adding suitable
elements for current collection known to those skilled in the art
to the stack structure thus constructed.
(Gas Conduit)
[0066] As shown in FIG. 1, a single cell 2 of the stack structure
20 is provided with the fuel gas conduit 16 for supplying the fuel
gas to the fuel electrode 7 and the air gas conduit 18 for
supplying the air gas to the air electrode 9. The patterns and
forms of these gas conduits 16 and 18 are not particularly limited.
In addition to the u-shaped form shown in FIG. 1 and the straight
form shown in FIG. 2, examples may include zigzag, radial, spiral
and various other patterns. Other known forms may also be applied
to these gas conduits in the SOFC. These supply parts 16 and 18 are
preferably hollow channels, and are preferably formed alongside the
separator 14. In the stack structure 20 of the present teachings,
as shown in FIG. 1, these gas conduits 16 and 18 have the pattern
of u-shaped channels, with the openings 17 and 19 preferably
opening only on opposite sides of the stack structure 20. This is
because this allows the seal parts 10a and 10b to be formed,
respectively, in the fuel electrode layer 6 and air electrode layer
8 only on the surface with the gas channel opening that needs to be
avoided.
[0067] As shown in FIG. 1, in the stack structure 20 of the present
teachings, a unit consisting of a single cell 2 combined with one
or two separators 14 preferably has a flat-plate overall shape.
With this structure of laminated flat plates, the stack structure
20 as a whole can be configured as a pillar, making it easier to
obtain good mechanical strength because stress is less likely to be
concentrated in certain areas. The stack structure 20 can also be
obtained with little peeling or breakage even if there is residual
stress or the like due to differences in thermal expansion
coefficient. In addition, the manufacturing process of the
laminated SOFC can be facilitated.
[0068] The channel forms of the fuel gas conduit 16 and air gas
conduit 18 may be the same or different throughout all single cells
2. For example, a stack structure 20 having both u-shaped channels
and straight channels is not excluded.
[0069] The number of the single cells 2 formed by lamination in the
stack structure 20 is not particularly limited. They are preferably
laminated so as to achieve the necessary mechanical strength.
(Laminated SOFC)
[0070] The laminated SOFC of the present teachings can be provided
with the stack structure of the present teachings. The stack
structure of the present teachings can be provided as necessary
with suitable parts such as a gas supply system for supplying the
fuel gas and air gas from a supply source to the stack structure, a
current collector, a casing and the like to construct a laminated
SOFC.
(SOFC System)
[0071] The SOFC system of the present teachings can be provided
with the laminated SOFC of the present teachings. A single
laminated SOFC can be used, but ordinarily one or a plurality of
modules each combining a plurality of laminated SOFCs are provided
so as to yield the desired power output. The SOFC system can also
be provided with known SOFC system elements such as a fuel gas
reformer, heat exchanger, turbine and the like.
(Method for Manufacturing Laminated SOFC)
[0072] As shown in FIG. 4, the method for manufacturing the
laminated SOFC of the present teachings comprises a step of
preparing a laminate as a precursor for the stack structure, and a
step of heat-treating the laminate. FIG. 5 describes one example of
this manufacturing process.
(Laminate Preparation Step)
[0073] The laminate preparation step is a step of preparing first
sheets comprising a solid electrolyte material as the material of
the solid electrolyte or a separator material as the material of
the separator, preparing second sheets having an electrode material
region comprising the fuel electrode material or air electrode
material and a seal material region for forming a non-porous seal
part equivalent at least in terms of thermal expansion and
contraction characteristics to the aforementioned solid electrolyte
or separator, and laminating these second sheets onto the first
sheets repeatedly to prepare a laminate. Since the laminate here is
the precursor of the stack structure, it is laminated with the
single cells being separated by the separators.
[0074] In the manufacturing process shown in FIG. 5, an evaporative
material layer for forming the air gas conduit is formed on a first
sheet comprising the separator material, after which a second sheet
having the electrode material region consisting of the air
electrode material and the seal material region consisting of the
solid electrolyte material is laminated. The first sheet comprising
the separator material can be obtained by making the separator
material explained above into a sheet by ordinary methods. Both the
first and second sheets are sheets of unfired ceramics that will be
converted to the desired ceramics by heat treatment after
lamination. Such a first sheet can be obtained for example by a
casting method such as tape casting in which a knife coater, doctor
blade or other applicator is used to sheet mold a slurry consisting
principally of a separator material with binder resin, organic
solvent and the like added in suitable amounts. The resulting sheet
is first dried by ordinary methods and then heat treated as
necessary to obtain a first sheet (unfired ceramic green
sheet).
[0075] A ceramic powder comprising a lanthanum-chromium perovskite
oxide and rare earth-doped zirconia is preferably used for the
separator material. Including rare earth-doped zirconia allows the
lanthanum-chromium perovskite oxide to be densely sintered even at
a firing temperature of no more than about 1400.degree. C., which
means that it can be co-sintered with the cell components. High
electrical conductivity can also be maintained. In this material,
the rare earth-doped zirconia preferably constitutes at least 0.05
mass % but no more than 10 mass % of the lanthanum-chromium
perovskite oxide ceramic. Below 0.05 mass %, the sintering
temperature will not be lowered sufficiently, while above 10 mass %
conductivity may be adversely affected.
[0076] Next, the second sheet is prepared. The second sheet is
provided with the air electrode material region and the seal
material region consisting of the solid electrolyte material. The
arrangement of the air electrode material region and seal material
region is determined by the design concept of the seal part as
explained previously with respect to the laminated SOFC of the
present teachings. Such a sheet of different regions can be
obtained by a method of sheet molding by means of dip casting or
other casting using a doctor blade or other applicator. That is,
slurries of different compositions are discharged simultaneously in
the casting direction, and applied in such a way that the different
slurry regions can be integrated without being mixed after casting.
Integral application of these regions of different compositions can
be achieved by adjusting the fluidity of the slurries for forming
the different regions. The resulting casted product can be dried by
ordinary methods and heat-treated as necessary to obtain the second
sheet.
[0077] The slurry for the air electrode material region can be
obtained by making the air electrode material described above into
a slurry by ordinary methods. A foaming material or the like can be
added as necessary to the slurry for the air electrode material
region. A suitable slurry using the solid electrolyte material is
used for the seal material region in this case, and this can be
used for casting.
[0078] The second sheet is laminated onto the first sheet prepared
in this way. The alignment of the second sheet relative to the
first sheet is such that the fuel electrode material region and
seal material region are arranged in accordance with the desired
stack structure. When laminating the second sheet for the air
electrode or other electrode onto the first sheet consisting of
separator material, an evaporative material layer patterned to form
the gas conduit is preferably applied before laminating the second
sheet. A pipe structure that allows passages of gas is formed by
heat treatment when the evaporative material layer is composed of
the material that is eliminated in the heat treatment step. The gas
supply structure can be easily formed if the patterns are the
patterns of the fuel gas and air gas conduits. By preparing the gas
conduits in this way, pipe structures can be constructed without
complicating the lamination process or affecting the mechanical
strength and the like of the stack structure.
[0079] Once the first and second sheets have been laminated,
another first sheet is prepared, and another second sheet is
laminated on this first sheet. For example, in the example shown in
FIG. 5, a first sheet consisting of the solid electrolyte material
is prepared, and a second sheet having the fuel electrode material
region and the seal material region is prepared. The solid
electrolyte material and fuel electrode material described above
can be made into slurries for the solid electrolyte material and
fuel electrode material slurries. A foaming agent or the like can
be included as necessary in the fuel electrode material in order to
ensure porosity after heat treatment.
[0080] The types of first sheet and second sheet to be laminated
are determined according to the final stack structure to be
obtained (structure of single cells separated by separators). The
same applies to the orientation of the sheets during lamination.
The lamination sequence in the lamination process can be any that
yields a stack structure, without any particular limitations. For
example, the first sheets and second sheets can be laminated one
after the other, or partial laminates can be prepared and then
laminated together.
[0081] The composition and arrangement of the seal material region
in the second sheet can be as explained previously with respect to
the stack structure of the present teachings. The various features
explained with respect to the stack structure of the present
teachings can also be applied to the gas conduit.
(Heat Treatment Step)
[0082] The heat treatment step is a step of heat-treating the
laminate obtained in the laminating step as a precursor for the
stack structure. Heat treatment is performed so as to sinter at
least part of the ceramic materials composing the laminate and
obtain the desired dense or porous fired body. Preferably, the
separator and all the cell components are co-sintered. Heat
treatment can be performed for example at a temperature of at least
1250.degree. C. but no more than 1550.degree. C., or preferably at
least 1300.degree. C. but no more than 1500.degree. C. At least
1300.degree. C. but no more than 1400.degree. C. is still more
desirable. Firing can be performed in air.
[0083] The sheets composing the laminate are integrated by this
heat treatment to yield the stack structure of the present
teachings. That is, a stack structure in which the single cells are
separated by separators and parts functioning as seal parts are
integrated with the fuel electrode layers or air electrode layers
of the single cells can be obtained all at once.
[0084] As described above, with the manufacturing method of the
present teachings it is possible to obtain the stack structure all
at once by preparing and laminating the sheets corresponding to the
separator, solid electrolyte, fuel electrode layer and air
electrode layer in the stack structure. That is, it is easy to
obtain a stack structure of the present teachings having various
advantages.
[0085] One embodiment of the present teachings was explained above,
but the present teachings is not limited thereby, and various
changes are possible to the extent that they do not deviate from
the intent of the present teachings.
(Electrode Sheet for Laminated SOFC)
[0086] An electrode sheet for the laminated SOFC of the present
teachings can have an electrode material region comprising a fuel
electrode material or air electrode material, and a seal material
region for forming a non-porous seal part in the laminated SOFC.
With the sheet of the present teachings, a seal structure can be
provided easily and reliably because a seal part can be formed
within either the fuel electrode layer or air electrode layer. In
particular, because the seal material region is equivalent at least
in terms of thermal expansion and contraction characteristics to
the solid electrolyte or separator of the laminated SOFC, it has
good integrity with the adjacent separator or solid electrolyte,
resulting in a stack structure with excellent mechanical
strength.
[0087] The various forms for the fuel electrode, air electrode,
separator, solid electrolyte and seal part explained above with
respect to the stack structure of the present teachings may be
applied to the electrode sheets of the present teachings. The
manufacturing method for the second sheet explained above with
respect to the laminated SOFC of the present teachings can be
applied to manufacturing the electrode sheet of the present
teachings.
[0088] The present teachings is explained in detail below using
examples, but the present teachings is not limited to these
examples.
Example 1
[0089] In this example, Ni/8YSZ cermet (Ni:8YSZ=80:20 (mole ratio))
was used for the fuel electrode, La.sub.0.8Sr.sub.0.2MnO.sub.3
(LSM) for the air electrode, 8YSZ for the electrolyte, and
La.sub.0.79Ca.sub.0.06Sr.sub.0.15CrO.sub.x (LCaSCr) for the
separator. Slurries of each were prepared, and the separator sheet
and solid electrolyte sheet were prepared by tape casting as green
sheets 20 .mu.m to 80 .mu.m thick. For the air electrode sheet, a
20 .mu.m-thick green sheet was prepared having an air electrode
material region with a seal material region consisting of separator
material at one end. For the fuel electrode sheet, a 20 .mu.m-thick
green sheet was prepared having a fuel electrode region with a seal
material region consisting of separator material at one end. The
slurry concentrations were adjusted for each sheet to obtain
uniform shrinkage of the green sheets during heat treatment.
[0090] These sheets were laminated as shown in FIG. 6, and fired in
air at 1400.degree. C. The resulting structure was integrated
without warpage, resulting in a highly integrated structure with no
peeling between layers. In the resulting structure, the fuel
electrode layer, air electrode layer and solid electrolyte were
each about 15 .mu.m.
[0091] From these results, it can be seen that a good laminated
structure without warpage can be obtained by laminating and firing
the various sheets used in the example.
[0092] The composition of a cross-section of the fired structure
was confirmed by energy dispersive x-ray spectroscopy (EDX). The
results are shown in FIG. 7. This shows that layers were formed
with the intended compositions for the separator, air electrode,
solid electrolyte and fuel electrode.
Example 2
[0093] In this example, carbon paste was screen printed when
laminating the separator sheet to the air electrode sheet and the
separator sheet to the fuel electrode sheet in Example 1, and
firing was performed as in Example 1. The resulting structure was
shown to have spaces formed in the regions where carbon paste was
applied, while still maintaining overall integrity as a structure.
This shows that fine gas channels can be formed using an
evaporative material.
Example 3
[0094] In this example, LaCaSCr powder was compounded with 3YSZ (3
mole % yttrium-stabilized zirconia) in amounts of 1%, 2%, 3%, 4%,
5% and 7% of the mass of the oxide powder and roughly 10 mass %
calcium nitrate in addition to these oxide powders, and mixed well
in a mortar. This mixed powder was molded in a uniaxial press (1300
kgf/cm.sup.2, 5 minutes), and fired for 5 hours in atmosphere at
1300.degree. C. A comparative example was also prepared by the same
operations but with no 3YSZ added (sample with 0 mass % calcium
nitrate-containing 3YSZ).
[0095] The volume and weight of the resulting sintered body were
measured, and the density calculated. The results are shown in FIG.
8. FIG. 9 shows the results of scanning electron microscope (SEM)
observation of cross-sections of the resulting sintered bodies (0
mass % and 1 mass % samples).
[0096] As shown in FIG. 8, the density of the
lanthanum-calcium-strontium-chromium oxide, which was 5.3
g/cm.sup.3 without added 3YSZ, rose to 6% with 1 mass % 3YSZ added,
and to 9% with 5 mass % added. As shown in FIG. 9, moreover, it was
confirmed by scanning electron microscopy (SEM) that adding a small
amount of 3YSZ resulted in finer and denser crystal grains.
* * * * *